Towed agricultural mowers typically comprise a mowing unit that is supported by a frame, typically in a manner that there are two basic positions. The first is a transport position wherein the mowing unit is in fixed position with the frame supporting its full weight. The second is the lowered operating position wherein it is able to float, move relative to the frame, with a portion of its weight carried by a suspension system to the frame (ultimately through the wheels to the ground). The remaining portion of the weight is transferred directly to the ground via a skid or sliding member. The weight, or force transferred directly to the ground via the skid is hereinafter referred to as ground pressure. The amount of ground pressure will affect the performance of the mower. Many designs provide an operator-adjustable suspension system. Suspension systems are designed to suspend a specific range of weight. The weight range corresponds to a large percentage of the weight of the mowing unit. In this way, the desired ground pressure is provided in order to minimize damage that the skid on the mowing unit may cause to the ground in comparison to allowing the full weight to act against the ground (that is, with no weight being carried on the frame and wheels).
The most common mowing units include a cutting apparatus, a crop conditioning apparatus and the drive train necessary to transfer power to both; the total weight can be significant. Thus, the suspension systems require the use of elements with correspondingly significant load bearing capacity, typically relatively large extension springs. Other suspension systems utilize other types of springs, including rubber torsion springs as disclosed in U.S. Patent Applications publication number 2003/0140610 to Boyko wherein a towed rotary mower uses rubber torsion elements mounted onto the frame, the rubber torsion elements supporting crank arms to support wheels and suspend the frame and mowing unit. U.S. Pat. No. 5,960,614 to Jones discloses a suspension for a mower that is mounted to a tractor with a frame that moves up and down to control the height of the mower, and a suspension element comprising a rubber torsion axle, used to urge one of two parallel linkages in a direction to support a mower unit attached to the frame with a four bar linkage. Neither of these configurations provides an operator control of the ground pressure.
A need thus exists for an improved suspension system for a mower that provides operator adjustment of ground pressure and that is adapted to optimize the mounting onto a trailed frame.